EFFECTS OF PHYSICAL FACTORS ON PHOTOSYNTHESIS BY THE ANTARCTIC LIVERWORT MARCHANTIA-BERTEROANA

Effects of irradiance, temperature and water availability on respirati on and photosynthesis in a maritime Antarctic liverwort, Marchantia be rteroana, were investigated. Carbon dioxide exchange was measured usin g an infra-red gas analysis system under controlled conditions. The re lationships between respiration, photosynthesis, irradiance and temper ature were modelled. Application of these models to year-round micro-c limate data provided an estimate of yearly net productivity of 823 (SE = 75) mg C . g(-1) ash-free dry weight. year(-1); this is somewhat hi gher than figures obtained for other Antarctic cryptogams. Desiccation had a highly adverse affect on Marchantia. Photosynthetic capacity wa s reduced below a water content of 12 g . g(-1) afdw. and there was on ly a limited recovery (ca. 10%) after dehydration. Freezing also cause d a great reduction in photosynthesis, although the model suggested th at photosynthesis at sub-zero temperatures is likely. It is suggested that seasonality in the photosynthetic capacity and the survival of su bzero temperatures might be important. It is concluded that Marchantia is a relatively productive Antarctic cryptogam that may dominate favo urable areas, but that its low tolerance of environmental stress, part icularly desiccation, limits its distribution to relatively mild habit ats.